Hitherto, the method of manufacturing molded parts buried in a thermosetting resin involves the steps of:
(1) putting parts to be buried into a heated die, PA1 (2) filling the die containing the parts with a curable thermosetting resin molding material by either an injection method or a transfer method to cover the parts with the resin, PA1 (3) curing the thermosetting resin in the die by heating to a temperature above the reaction starting temperature, and PA1 (4) finally completely curing to finish the curing reaction, and removing the molded parts from the die. PA1 an unsaturated alkyd resin, and PA1 a crosslinking monomer to be crosslinked to the unsaturated alkyd resin, PA1 in which the crosslinking monomer includes a first crosslinking monomer having a [C.dbd.C] group, a [--CO.sub.2 --] group and a [--OH] group. These groups are, respectively, an ethylenically unsaturated group, a carboxyl group, and a hydroxy group. PA1 (a) a cured resin resulting from curing a molding composition comprising PA1 (b) an electronic component covered with the cured resin (a). PA1 (a) covering with a molding composition the outside of an electronic component that can be heated, PA1 (b) feeding power to the electronic component to generate heat in the electronic component, and PA1 (c) curing the molding composition using the heat generated in the electronic component.
In order to shorten the curing time and enhance productivity, it is necessary to raise the temperature of the molding material as promptly as possible above the reaction starting temperature. To this purpose, by preliminarily heating either the parts to be buried or the molding material, one hopes to decrease the curing time.
In the known conventional method of preliminarily heating the parts to be buried, when the parts are heated to a temperature close to the reaction starting temperature of the thermosetting resin, curing starts during the step of injecting the mold into the die in which the heated parts are placed. As such, the molding material is not completely injected into the die, or the molding material is not completely charged into the parts. Or, the cured molded parts are cracked, and complete molded parts are not obtained. Thus, the preliminary heating temperature of the parts to be buried cannot be raised too high.
Moreover, the reaction starting temperature and the curing time of the thermosetting resin depend greatly on the type of polymerization initiating agent, such as a peroxide, added to the resin. Hence the curing time can be controlled by selecting the type of polymerization initiating agent. However, the polymerization initiating agent to decrease the curing time generally causes a simultaneous drop in the reaction starting temperature. This means that the storage period of the molding material is shorter, and the storage stability of the molding material is inferior.
It is hence an object of the present invention to provide a molding composition having enhanced productivity and a method of manufacturing molded parts from that molding composition.